Protector for electric circuits



1, 1953 J. c. LEBENS, JR 2,648,739

PROTECTOR FOR ELECTRIC CIRCUITS Filed April 50, 1951 J ENTOR JO/"7. C. Lebens Jr: BY

ATTORAZE'Y Patented Aug. 1l, 1953 UNITED STATES PATENT OFFICE;

John" C; Lebens, Jr., University'City, Mo., assignor to McGraw Electric Company,- Elgin, 111., a corporation of Delaware Application April 30, 1951, Serial No. 223,720

20 Claims. 1

This invention relates to improvementsin protectors for. electric: circuits- More-particularly, this invention relates to improvements in protectors for electric.circuitsnwhich areequipped with indicators that provide,.at all times, a visual indication of thecondition'of such protectors.

It is therefore an object of the present invention to. provide an improved protector for electric circuits. which is equipped with an indicator that provides, at all times, a visual indicationof the condition of such protector.

Protectors for electric circuits are customarily enclosed within casings; and in many instances the casings consist of hollow tubes of insulating materialwhich telescope over the protectors for electric circuits, and ferrules'of metal that close theends of .those tubes. Thecasings protect the component partsof the protectors for electric circuits from injurywhich" theymiglit otherwise sustain through contact withforei'gn ob'ects, and they also protect nearby" individuals and objects from'the'heat'and flame'which" often accompanies thecircuit protecting operation of protectors"for'='electric circuits.

The hollow tubes, which are part of the casings forsu'ch protectors for electric circuits, are often composed of opaque insulating material'such as fiber; and it is therefore'usually impossible to determin -visually the-condition of the protectors for electric circuits; As a result, maintenance men frequently must test a number of protectors forelectric circuitsbefore then can locate the particular protector that has actedto open the circuit. This is a-time-consumingprocess; and it at bestahit-or-Iniss process.

In recognition of this problem, various attempts have been made todevelop operative andsuccess' ful protectors for electric circuit which had indicators that could provide a visual indication of the condition' of the-protectors for electric circuitsxWhile: many'suchprotectors for electriccircuits were proposed, only a few wereactually manufactured; and few, if any, of 'such protectors are now being-manufactured. The indicators of such protectors for electric circuits usually consiste'ds'of small diameter. wires which extended between the metal ferrules of the'casings of the protect'ors and which held cantilever springs or spring-mounted discs in retracted position; those wires'fusing whenever the protectors operated to' open the circuit, and thus permitting the springs and'discs'to' move 'toexten'ded position Where they could'b'e' seen. The indicators of such protectors for'telectric circuits often iailed'to operate at all, and in some instances they operated prematurely andgave false indications of the condition .of the protectors.

The defective operation of the indicators for these protectors for electric circuits frequently was caused by variations in the spacing between the'metal ferrules of the casing-s of the protectors; such variations in'spacing being caused by expansion or contraction of the tubes of the casings for the protectorsfor electric circuits The expansion or contraction of'the tubes of such casings is unavoidable where those tubes are made of fiber, since fiber expands and. contractsas the moisture in the air varies the moisture content of the fiber; and the expansion or contractionof the tubes stretches or'slackens the small diameter wires extending between the'ferrules at the ends of these tubes. Thestretching ofthe small diameter wires of the indicator could either break those wires andthus free the springs or discs prematurely, or they could'provide such an elongation of those Wires that the springs or discs could move appreciable distances toward extended p0sisition when the tubes next contracted; 'Alternatively, the'stretching ofthose wires could distort or jam the springs of the indicators. The

slackening of the wires could permit the springs or discs to move toward extended position. In anyof these events, defective or false indications of the condition of the protectors for electric circuits can not be avoided. Such false or defective indications are worse thanno indications at all, because they mislead the maintenanceman when he attempts to locate aprotector which has -op-' eratedto open the circuit;

. The presentinventio'n provides a protector for electric circuits which will not give false or de fective' indicationst of the condition ofsaid'prm tectorysuch protector havingian indicator with elongated telescoping elements. are biased for movement to extended position-by a spring but are normally held in retracted positionby a small diameter wireg'and the telescoping elements and the spring can easilycompensate forany expansion or contraction of the tube-of the casing of the protector. Consequently, the indicator is kept from givingfalse or premature indications of the condition of the protector for electric circuits. It istherefore an object ofthe present invention to provide an indicator for protectors'for electric circuits which has elongated telescoping elements anda spring biasing those elements toward extended position.

In many protectors for electric circuitsthe elongated telescoping elements and the springs can provide full. compensation for the expansion andcontraction of the casings. However, in

These elements some protectors for electric circuits which have elongated casings, the amount of expansion and contraction that must be accommodated is excessive. The present invention makes successful indicator operation possible in such protectors by making the small diameter wires of the indicators for such protectors wholly independent of the expansion or contraction of the casings of those protectors for electric circuits. The present invention does this by providing a short closure for the small diameter indicator wires, and by mounting that closure so its length will not be affected by changes in the length of the casing for the protector for electric circuits. It is therefore an object of the present invention to provide a short closure for the indicator wires of a protector for electric circuits which can be mounted so its length will not be affected by changes in the length of the casing of such protector.

Indicators have been known to give false inclications in protectors for electric circuits because the resistances of the protectors for electric circuits could increase, with overloads, to the point where the indicator wires carried enough current to become hot and heat the springs associated with them. In some instances, where the over loads recurrently reached values that normally would cause the protector to open the circuit but would subside before the protector would have to operate, the indicator wires have become hot enough to take the temper out of the springs associated with the indicators. In such instances the springs would be unable to move the indicator to indicating position when the protector for electric circuits did open the circuit. The present invention obviates excessive heating of the springs associated with the indicator wires of protectors for electric circuits by reducing the overall length of the fusible portions of the indicator wires, and by surrounding the springs with relatively massive heat absorbing elements. The reduced length of the fusible portions of the indicator wires reduces the amount of heat generated by the indicator wires, and the surrounding of the springs with heat absorbing elements quickly dissipates heat from the springs. It is therefore an object of the present invention to reduce the length of the fusible portion of the indicator wires of protectors for electric circuits,

and to surround the springs associated with those wires by heat absorbing elements.

To operate effectively, an indicator wire must have a smaller current carrying capacity than the protector for electric circuits with which it is used. customarily this means that the indicator wire must be of very small cross section. Such a wire is fragile indeed, and it could become bent, pinched, or broken durin the assembly of the protector for electric circuits with the casing for such protector. The present invention obviates any such pinching, bending or breaking of the indicator wire by disposing that wire within a closure which in turn is disposed Within the casing for the protector for electric circuits. This closure not only protects the wire against pinching, bending or breaking, but it provides an obstruction-free pathway for the indicator wire to follow when the telescoping elements move it as they move to extended position.

Some indicators which have been proposed for use with protectors for electric circuits would be mounted on the exterior of the casings of the protectors. Such indicators are subject to being broken, bent or distorted by contact with foreign objects; and they would then be prevented from operating properly. This is objectionable. The present invention obviates this objection by disposing the indicating portions of the indicator wholly within the casing of the protector for electric circuits.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description two preferred embodiments of the present invention are shown and described, but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing Fig. 1 is a cross-sectional, side view of a protector and indicator that is made in accordance with the principles and teachings of the present invention, and it shows the indicator in retracted position,

Fig. 2 is a partially broken-away, side elevational view of the protector and indicator shown in Fig. 1, and it shows the indicator in extended position,

Fig. 3 is a cross-sectional, side view of the telescoping elements and spring of the indicator shown in Figs. 1 and 2, and it shows that element in retracted position,

Fig. 4 is a cross-sectional, side view of the telescoping elements and spring shown in Figs. 1-3, and it shows those elements in extended position,

Fig. 5 is a cross-sectional, side view of another form of protector and indicator, and

Fig. 6 is a cross-sectional, side view of the telescoping elements, spring and fusible wire of the indicator shown in Fig. 5.

Referring to the drawing in detail, the numeral I0 denotes a cylindrical tube which is made of an insulating material such as fibre. The numeral I2 denotes a metal ferrule which telescopes over the left hand end of the tube I0; and the numeral I4 denotes a ferrule I4 which telescopes over the right hand end of the tube ID. The tube Iii and the ferrules I2 and I4 constitute the casing for a protector for electric circuits; the ferrules I2 and I4 also constituting the terminals for that protector.

Ferrule I2 has an elongated opening I6 therethrough at the approximate center thereof, and it has an opening I8 therethrough adjacent one side thereof. Ferrule I4 has an elongated opening 28 therethrough adjacent the center thereof, and it has an opening 22 therethrough adjacent one side thereof. When the ferrules l2 and I4 are telescoped over the opposite ends of the tube I0, the openings I6 and 20 should be aligned and registered, whereupon the openings I8 and 22 will be in register.

Supports 24 and 26, in the form of discs, are disposed within the tube IIJ intermediate the ends of that tube. These discs are of insulating material such as fibre, and they have openings therethrough, not shown, which receive and support fusible links 28 and 30. The fusible links 28 and 39 are wider than they are thick and have an elongated cross section. Fusible link 28 will extend from the opening I 6 in ferrule I 2 through the opening in disc 24 to one end of a generally U-shaped metal heat absorber 32. A loop-like projection 33 is punched from the body of the heat absorber 32, and the right hand end of the fusible link 28 is inserted between that projection and thetsbody' ofthe' heat v absorbing 'member" 32:

Solder 35 is then used to provide a fully-intimate.-

electrical connection .betw'eenvthe fusible slim-1:628 and? thecheat absorber. 3-23 dis'c' '26 and overlies the right hand endiof the heat absorbing :member: 32.

A: light-weight. connector 34 extends 5 between? the: left hand end' of the fusible. link 30: and the righ't hand end' of the. heat absorbing member" 32, and. normally. maintains them in electrical connection. A spring: 36 is? secured' to: the. left hand end of the connector and to.:a hook-38' which is iriveted to the disc 24. 'The spring36 link" 30. and heatabsorbing member 32; This opens; the protector and" prevents :further current." flow- -through it between ferrules. l2; and HL.

Eitherof; the fusible links. 28. or 30 can respond to. heavy overloadsror short circuits to fuse and thereby open:the circuit.v

A closure. 40, in the form .of'an elongated tube! of insulation,- is:-- disposed: within the casing. for theiprotector. for. electric circuits;

4!! being held againstmovement by theconjoint action of discs 24and Hand tube 20'. Thediscs 24- and 26: are dimensioned. so-theends of'the closureAB will be in register with the openings [8 and'i22 in ferrules l2 and lli'wheneverthe ends of the fusiblelinks'23 and3il are placed inregisten withthe'openings IGIand-IZB in ferrules l2and 14i- Thus-the discs 24 andzz 6 facilitate rapid assembly of the protector, indicator and easing shown'in Figs. 1and'2f. The closure lo'is free of obstruc tion'sithroughout': its length; and it communicatesdirectly with'the'openings I8 an'd' -22. i

The numeral 42;den0tes a sleeve of'metal which has'aiflange i' l at oneend thereof and which has aperforated end wall atitlie other end thereof Sleeve 42 is dimensioned so it can'telesc'opewithin thefrighth'and end of the closure 40, butthe flange 44 is dimensioned so it will'engage the right hand end of closure 4:?- and prevent unlimited movement'of the sleeve' lz inwardlyof closure. 40: An elongated pin A8 extends through" the perforated-end Wall 46 of the sleeve; and

thatqain'ha's aplanished end 59 with a hole'there through; In addition, that pin has an enlarged head t52'at its'other end; Prior to the'planis'hing" of the :lefthand end of the pin 48, a helicalspring" 54' isslipp'ed over the left hand end'of the pin;

and'the left hand end of the pin is passed through the opening in the perforated end wall 461 of the sleeve 42. The planishingjof the left hand' end of pin 48 maintains the sleeve; the pin 48 andthe spring 54' in assembled relation. The head 52 of pin 48 is'p'aintedor otherwise provided with a color and'hue which isdiiferent from the color and hue of the tube Hi and of the'fe'rrule l4. 7 v

A small' diameter, readily fusible wire 56 of low current-carrying capacity is threaded through.

the openingin thee plan'ished end 500i" pin '48,

andi-the two-'endsof thatwire'are passed through closure 49. The fusible'ilinks 28 and 39,-the-heat absorber 3-2, the: connector "34 and the" spring" 35 Theright hand end of thefusiblelink 30'is" in registerwith thetopen ing 20 in ferrule Id, and the left handjend'ofi that'fusiblelink= extends through the .opening in;

This closure: will restin andbe confined by holes or notches inxtliezedges ofthetdisc's'2'4'and26; the closure constitute a "protector for electricr circuitsri- 'The sleeve 142; the pin 485 the. spring. Sitanditlfe wire? 56 constitut'e': an" indicator: The protector'isririie if tia'lly assembled with the discs and? 26; the:=' indicator is initially assembled with the closure".

40, the closure'x liliis "then assembled 'witli the discs" 24'and 26,- and'ithen .the discs 24" an'd"2'6-'with the: protector andithe closure wmounte'dthere'onsare2 teleseoped within the tube: I 0. Ferrule' Hris'then set soithe. elongated 'open'ing l'fi therethrou'ghreg f isters' With'the elongated cross section of fusible" link (ill; and 'that ferrule is'telescopedoven the right hand endiof'tube- Ill. The pin 48 will 'slip'-- neatly throughopening'ZZin ferrule 14 since the Y placing-of opening 23in register with fusible-link 30.simultaneously'placed closure in register f Within" the casing! of the'protector for' electriccircuits but .is. immediately adjacent the opening through whichthat head can "move to the-exterior of such casing; Once this initial-position of pinr48.liasibeenattained; the-left hand en'ds' of wire: 5fi'lare'soldered to ferrule [2 bymeans or so1der58. This solderwill also electricallycoh nest-"the. leftfhandz end I of fusible link 28 'to 'the' ferrule 12 and-to thewire 56. "Solder fill is then applied-toferruleldarid to the righthand end of fusibleilinl30 This solder'will'connect fusi ble link 30. directly toferrule [Aland indirectly to sleeve"42-;

Theipin willirestfagainst some part'of the 'perforated end" wall .46 of the sleeve l-2i becausetlie actiona-oft the'sprin'g 54"- willbe to shift-"the'pinagainst; some partfof thatendwalli; Consequently;: current can. flow from" the sleeve" 42* directly into fthei pin llland then to -the "wire 56% Asecondary'electrical patli of subordinate naturewill existbetweritsleve 42'"and pin'48 throughthespring I54; However, becauseof the length "of the-springfil; the major p'ortion' of' the current flowing from sleeve -42 to I pin 48 will pass directly through tli'e'en'd w all t'o'th e -pin 48.

fcurrentican flow fromthefrrule l2-to the ferrule-14: either through fusible link' 28; Heat absorber'32, connector" 34 and fusible link 3'll 'or throughwire' 56-, pin 48, and. sleeve. 42. The Wire 56, the. pin 48 and the sl'eeve"42;thus 'con stitute -an.- electrical conductor: in para-Hell relation With the protector for electric circuitsc'onesisting of fusible links 28- andSU, heat absorbers" 32, connector. 34,.and spring36. The protector" will be ableltocarr'y current continuously-under normalconditions of load, butthe wire Sit-Will fuse instantlywhen the protector. opens the circuit. 'Fusion ofwire 56' will free pin .48-for. move-- ment outwardly through opening 22 to the .position"shown in Fig. 2. The pin 48, its enlarged head '52, and the righthand. end of spring -48. thus provide a'visua'l'indication of the condition of the-protector.

By mak'ingtlie" enlargedheadlEZ of the .elon=. gated-pin ltl'of a color or hue diiferentffrom. the coloror hue oftube m and ferrule m, the

present invention makes it possible for the user to see that enlarged head when it is wholly within the casing for the protector, as well as to see it when it is wholly outside of that casing. If the enlarged head 52 could not be seen when it was wholly within the casing for the protector, the user might believe the indicator had gotten lost or he might believe that the opening 22 had been formed in the ferrule l4 by mistake and that the protector did not have an indicator. While the enlarged head 52 of pin 48 can be seen in its retracted position when the protector is viewed from the end, that protector can not be seen in its retracted position when the protector is viewed from the side. Since protectors are most frequently viewed from the side, there will be no likelihood that the user could mistake retracted for extended position. A user, viewing the protector in a normal manner will be able to see the pin 48 and its enlarged head 52 only when the protector for electric circuits has opened the circuit through it and the Wire 56 has fused.

The closure 40 protects the necessarily thin and delicate wire 56 from abuse during the insertion of the protector into the tube [8. Moreover, it keeps the filler material, which will be used to surround the fusible links 28 and 38, from working its way to the sleeve 42 and then working through the hole in the perforated end wall 46 of that sleeve. If that filler material were to get into the sleeve 42, it could interfere with the telescoping movement of pin 48 and spring 54. If the tube In expands in length, the wire 56 will not be subjected to breaking stresses because the sleeve 42 and the pin 48 are sufficiently long that the pin 48 can move further into the sleeve 42 and compensate for the expansion of the tube l8. If the tube shrinks, the enlarged head 52 of the pin 48 will not project through the opening 22 because that head is initially positioned a distance inwardly of the ferrule 14. Consequently, expansion and contraction of tube I 6 will not interfere with eifective operation of indicator, and. will not cause premature or false indications of the condition of the protector.

The cross sectional area of the sleeve 42 is considerably greater than the cross sectional area of the two lengths of wire 56. Accordingly, the sleeve 42 will generate practically no heat as current flows through it. Similarly, the pin 48 has a cross sectional area which is vastly greater than the cross sectional area of the two lengths of wire 56, and thus pin 48 will generate virtually no heat as current flows through it. The overall result of the dimensioning of sleeve 42 and pin 48 is that the spring 54 can remain cool even though the wire 56 would tend to heat. It should also be noted that the wire 56 constitutes a two strand conductor which is shorter than the protector itself. By being shorter than the protector, the two strand conductor has a shorter effective heat generating length than the protector would have if the protector were made throughout of resistance material. Many protectors are made of resistance material throughout and they are often referred to as straight through link-type fuses. With such protectors, the amount of heat generated by the wire 56 will be quite small relative to the heat generated by the protector itself, and the amount of heat generated by the pin 48 and the sleeve 42 will be so very small that it can be neglected. Consequently, the spring 54 will be protected from heating even if the resistance of the protector rises appreciably on 8 overloads and thus increases the heating done by the wire 56.

The elongated pin 48 and the enlarged head 52 thereof constitute the most prominent part of the visual indication provided by the indicator disclosed herein. However, the spring 54 does act as an indicator too because it projects from the ferrule l4. While the pin 48 could be modified by eliminating its planished end 58 and by making that pin short enough to be wholly within the sleeve 42 when in retracted position, so the spring 54 would be the principal visual indication provided by the present invention, it is desirable to use the pin 48 in the form shown. The

planished end prevents separation of the pin 48 from the sleeve 42 and thus assures a continuing visual indication of circuit-opening operation of the protector. In the absence of the planished end 58, the pin 48 could become lost and then the user might not look at the ferrule 14 from the end; and if he did not do so he would not realize that the protector had opened the circuit. Thus the planished end 58 of the pin 48 positively assures full and complete visual indication of the condition of the protector for electric circuits.

In Fig. 5 the numeral 62 denotes a tube of insulating material such as fibre. This tube is provided with metal ferrules 64 and 66 which have elongated openings therein. The ferrule 66 has a second opening therein adjacent one side thereof. Terminals 68 and 48 of a protector for electric circuits are normally disposed within and supported by the elongated openings in ferrules 64 and 66. Fusible links 12 and 14 are secured to the inner ends of terminals 68 and W by rivets and solder. The inner end of the fusible link 72 extends through an opening, not shown in a disc-like support 84 and is soldered and riveted to one end of a heat absorber 16. The inner end of the fusible link 14 extends through an opening, not shown, in the disc-like support 86 and overlies the other end of the heat absorber 14. A connector 18 is soldered to the link 14 and to the heat absorber 16, and that connector is biased for movement out of engagement with link 74 and absorber 16 by a helical spring 88. The helical spring is placed under tension by being slipped over a hook 82 which is riveted to the disc 84.

A closure 88 of tube-like configuration is supported by a slot, not shown, in the periphery of the disc 86. That slot is dimensioned so the closure 68 will be held tightly whenever the disc 86 is disposed within the tube 62. The left hand end of the closure 86 bears against a metal support 96 which has a length greater than the inner diameter of the tube 62 but which has an outer diameter less than the inner diameter of ferrule 66. The support 86 has an opening therethrough and that opening receives a sleeve 42 identical with the sleeve 42 of Figures 1, 3 and 4. A washer of insulating material is interposed between the support 96 and the flange 44 on the sleeve 42. The sleeve 42 will snugly fit within the opening in support 96 and will thus be in electrical connection with that support 86. The support 96 will fit snugly within the ferrule 66 and will thus be in electrical contact with that ferrule. Moreover, the support 96 will fit snugly within an opening in the terminal 18 and Will be in electrical connection with that terminal. Consequently, the support 66 acts to place the sleeve 42 in electrical connection with the terminal 16 of the protector for electric circuits.

The sleeve 42 carries an elongated pin 48 simithat has a casing, spaced terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor including a stationary element and a movable element biased for movement relative to said stationary element, said movable element of said electrical conductor normally being held stationary in retracted relation with said stationary element by other portions of said electrical conductor but telescoping to extended relation with said stationary element to serve as said indicator whenever said electrical conductor fuses, said stationary element being cylindrical and being disposed inwardly of and immediately adjacent an opening in said casing for said protector for electric circuits, said movable element normally having a substantial portion thereof telescoped within said stationary element but being movable to project said substantial portion outwardly of said casing.

5. In an enclosed protector for electric circuits that has a casing, spaced terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor including telescoping elements, said elements being adapted to retract telescopically relative to each other and thereby maintain certain portions of said electrical conductor taut despite variations that may occur in the physical dimensions of said casing during storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elements to project outwardly of said casing for said protector for electric circuits and serve as said indicator Whenever said electrical conductor fuses, said telescoping elements being substantially enclosed within a closure, said closure for said telescoping elements being disposed within said casing for said protector for electric circuits.

6. In an enclosed protector for electric circuits that has a casing, spaced terminals, a fusible portion electrically connected between said terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents when ever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor being spaced away from said fusible portion, said electrical conductor including telescoping elements, said elements bein adapted to retract telescopically relative to each other and thereby maintain certain portions of said electrical conductor taut despite variations that may occur in the physical dimensions of said casing during storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elements to project outwardly of said casing for said protector for electric circuits and serve as said indicator whenever said electrical conductor fuses, said electrical conductor including the telescoping elements thereof being substantially enclosed within a closure, said closure for said electrical conductor being disposed within said casing for said protector for electric circuits.

7. In an enclosed protector for electric circuits that has a casing, spaced terminals, a fusible portion electrically connected between said terminals, and an indicator that is adapted to indicate the response of the protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the impprovement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor being spaced away from said fusible portion, said electrical conductor including telescoping elements, said elements being adapted to retract telescopically relative to each other and thereby maintain certain portions of said electrical conductor taut despite variations that may occur in the physical dimensions of said casing during storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elements to project outwardly of said casing for said protector for electric circuits and serve as said indicator whenever said electrical conductor fuses, said telescoping elements being substantially enclosed within a closure, said closure for said telescoping elements being disposed within said casing for said protector for electric circuits, said closure for said telescoping elements being free of obstructions to the telescoping movement of said elements.

8. In an enclosed protector for electric circuits that has a casing, spaced terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a currentcarrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor including telescoping elements, said elements being adapted to retract telescopically relative "to each 'other and :thereby maintain certain portions of said electricalhconductor taut despite variations jthatgmay occur in the physical. dimensions'of said casing during storage and .use, i said telescoping elements being adapted to extend: telescopically and permit one --.of saiditelescoping elements to-project outward- -;ly of said-casing for said protector for'electric circuits and serve as said indicator whenever '9. In an enclosed protector for electric circuitsthat has a casing, spaced terminals, a fusi- .ble' portion. electrically connected :between said aterminalsyand arr-indicator that is adapted to indicate the, response of said protector for elec- .tric circuits-tea predetermined electrical con- 'dition in the circuit that said protector for elec- "triccircuits protects, the improvement which -..comprises a current-carrying electrical conductor that iselectrically connected in parallel re- -.lation with said protector for electric circuits, zsaid electrical conductor being subject to fusing :currentrwhenever said protector for electric cir- -:cuits:responds to saidpredetermined electrical condition in said circuit, said electrical conductor being spaced away-from said fusible portion,

said electrical conductor including an elongated pin-biased for movement outwardly of said casing for said protector for electric circuits, said pin normally being held retracted within' said casing for said protector for electric circuits but being free to move outwardly of said casing for said protector for electric circuits upon the fus- .:ing of 'said electrical conductor.

:-10.'In an enclosed protector for electric cir- -cuits that has a casing, spaced terminals, and an indicator thatisadapted to indicate the response of said'protector for electric circuits to a'predetermined electrical condition in the circuit tith-at said protector for electric circuits protects,

the improvement which comprises a currentcarrying electrical conductor that is electrically --connected in parallel relation with said protector for electric circuits, said electrical conduc- 1 tor". being subject to 'fusing currents whenever i said :protector for electric circuits responds to 'said predetermined electrical condition in said "circuit, said electrical conductor including an elongated pin, a spring, and a stationary memher" which normally confines an appreciable por- -tion of said pin and said spring, said spring biasingsaid portion of said pin outwardly of said stationary member, said pin and said spring being dimensioned relative to said stationary mem- 'berso-whenever said spring is compressed by the retraction of said pin within said stationary member, said spring is not fully compressed but can yield further to compensate for variations in the physicaldimensions of said casinglduring "storage and use.

11. In an enclosed protector forelectric circuits that has a casing, spaced terminals, and an indi-= tcator that;isz adapted toindicatethe response-bf I .said protector, for; electriczcircuits to;a:-:predeterminedelectrical conditionin thecircuitithatisaid protector for. electric circuits protects, the .im-

provement which tcomprises :acurrent-narrying electrical conductor :thatris -'.alectrica1ly :connected in parallel a relation, with said 'sprotectorvfor electric: circuits; said electrical; conductor being subject ;to :fusing' :zcurrentss rwhenever said, protector for electric circuits .respondsrto :said predetermined 1 electrical condition in .-,:'said- :circuit, vsaid .electricallconductor includingianeelongated pin ..biased for movementroutwardly: 0f.=:said casing :for zsaid' protector for :electric circuits; said pin; normally 1 being ;:held :retlia'cted within csaid casing forz-said protector; ionelectric circuits; but "being free :to movezoutwardly ottsaidacasing; for said protector for, electric circuits :upon theiusing .aofl said electrical/conductor, said electrical conductor including :a :stationary member; :that

; :norma-lly encloses :a, substantial t portion =,of::sa-id pin.

12. In an enclosed protector for; electric'circuits that has: a...casing,: rspacedilterminals, ca fusible portion electrically. connected ,between said terminals, and: an; indicatorthat is. adapted toindicate the response of-.said protectorforielectric circuits to a predeterminedelectrical ,condition in the circuit thatsaidprotector forielectriccircuitsprotects, the. improvementv which comprises a current-carrying ..'electrical: conductor: that iis electrically connected :in =parallel :relatiomwith said protector for electriccircuits, said: electrical conductor being subjectto. fusing currents awhenevervsaid protector forrelectric circuitssresponds to said predetermined electrical-condition inisaid circuit, said electrical conductor sheing ,ssp'aced away, from said "fusiblezportion, -'.said.. electrical conductor. including :an elongated pin; biasedlfor movement outwardly of said casingurorfsaid protector forelectric-circuits said:pin normally being held retracted ::within .said casing form said protector for electric circuits.but,,:being .free t=o move outwardly ofsaidcasing vfor saidzprotector for electric circuits upon the :fusingofisaidelectri-cal conductor; said electrical. conductor including a stationary -member that. normally.- encloses a substantial :portion a of said pin, and a spring that" isv disposed within; said stationary :member and surrounds said substantial sportioni of said pin.

13. In an enclosed protector for. electric circuits that has'a casing, spaced terminals; and: anindicator that is adaptedto indicate the response-of said protector for electric circuits to r a. predetermined electrical conditioniin the circuit that: said protector for electric circuits protects,- thezimprovement which comprises 'a current-carrying electrical: conductor that is electricallycconnected in parallel relation with said;protector-fonelectric circuits, said electrical conductor beingsubject to fusing currents wheneverasaid protector for electric circuits responds to 1 said predetermined electrical condition in I said circuit, said electrical conductor including -telescopi-ng-=ele- 'ments, said elements being adapted to retract telescopically relative'to each other and thereby maintain certain portions of said electrical conductor taut despite variationsthat may-occur in the physical dimensions of said casingduring storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elementsto project-outwardly or said .casing ,forasa-idi protectorgf'or; electric .cir-

cults and serve as said; r-indicatorpwheneyerr said Telectrical conductor fuses, said telescoping elements being substantially enclosed within a closure, said closure for said telescoping elements being disposed within said casing for said protector for electric circuits, said closure for said elements being much shorter than said casing for said protector for electric circuits to limit the expansion and contraction of said closure.

14. In an enclosed protector for electric circuits that has a casing, spaced terminals, a fusible portion electrically connected between said terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conspring is compressed by the retraction of said pin within said stationary member, said spring is not fully compressed but can yield further to compensate for variations in the physical dimensions of said casing during storage and use, said spring normally biasing said pin against and into electrical contact with said stationary member whereby said spring is largely free from current flow therethrough.

15. In an enclosed protector for electric circuits that has a casing, spaced terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, a support that engages said casing and said protector for electric circuits and holds said protector for electric circuits in spaced relation to said casing, and a closure for a portion of said electrical conductor, said support holding said closure for said portion of said electrical conductor in predetermined relation to said protector for electric circuits and to said casing for said protector for electric circuits.

16. In an enclosed protector for electric circuits that has a casing, spaced terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, a

closure for said electrical conductor, an opening in said casing for said protector for electric circuits, and a support, said support engaging said closure for said electrical conductor and said casing for said protector for electric circuits to place said closure for said electrical conductor in register with said opening in said casing.

17. In an enclosed protector for electric circuits that has a casing, spaced terminals, a, fusible portion electrically connected between said terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor being spaced away from said fusible portion, said electrical condutor including telescoping elements, said elements being adapted to retract telescopically relative to each other and thereby maintain certain portions of said electrical conductor taut despite variations that may occur in the physical dimensions of said casing during storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elements to project outwardly of said casing for said protector for electric circuits and serve as said indicator whenever said electrical conductor fuses, said telescoping elements having interlocking surfaces thereon whereby said elements are always held in assembled relation.

18. In an enclosed protector for electric circuits that has a casing, spaced terminals, and an indicator that is adapted to indicate the response of said protector for electric circuitsto a predetermined electrical condition in the circuit that said protector for electric circuit protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, a closure for said electrical conductor, said closure being disposed within said casing for said protector for electric circuits.

19. In an enclosed protector for electric circuits that has a casing, spaced terminals, a. fusible portion electrically connected between said terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parrallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electrical condition in said circuit, said electrical conductor being spaced away from said fusible portion, said electrical conductor including telescoping elements, said elements being adapted to retract telescopically relative to each other and thereby maintain certain portions of said electrical conductor taut despite variations that may occur in the physical dimensions of said casing during storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elements to project outwardly of said casing for said protector for electric circuits and serve as said indicator whenever said electrical conductor fuses, said one element having a color which is differ ent and distinctive from the color of said casin and terminals of said protector for electric circuits.

20. In an enclosed protector for electric circuits that has a casing, spaced terminals, a fusible portion electrically connected between said terminals, and an indicator that is adapted to indicate the response of said protector for electric circuits to a predetermined electrical condition in the circuit that said protector for electric circuits protects, the improvement which comprises a current-carrying electrical conductor that is electrically connected in parallel relation with said protector for electric circuits, said electrical conductor being subject to fusing currents whenever said protector for electric circuits responds to said predetermined electri- 18 cal condition in said circuit, said electrical conductor being spaced away from said fusible portion, said electrical conductor including telescoping elements, said elements being adapted to retract telescopically relative to each other and thereby maintain certain portions of said electrical conductor taut despite variations that may occur in the physical dimensions of said casing during storage and use, said telescoping elements being adapted to extend telescopically and permit one of said telescoping elements to pro- J'ect outwardly of said casing for said protector for electric circuits and serve as said indicator whenever said electrical conductor fuses, said one element normally being disposed wholly within said casing for said protector for electric circuits.

JOHN C. LEBENS, JR.

References Cited in the tile of this patent UNITED STATES PATENTS Number 

